1. Field of the Invention
The present invention relates to a print hammer for use in a printing mechanism.
2. Description of the Prior Art
In high-speed, moving-type impact printers of the kind typically employed in data processing systems, a separate print hammer is situated at each print position across a row of type. Hammer bank assemblies for this purpose are described in U.S. Pat. Nos. 3,643,595 to Helms et al and U.S. Pat. No. 3,983,806 to Ishi, and in copending U.S. Patent Application Ser. No. 065,766, filed Aug. 20, 1979, all assigned to Dataproducts Corporation, the assignee of the present invention.
Such hammer bank assemblies utilize a plurality of print hammers each having a flat, electrically conductive coil disposed in a generally rigid housing or body having an impact tip at one end and supported by a pair of crossed spring wires at the other end. The springs provide electrical contact to the coil, and air in restoring the hammer to its rest position subsequent to impact. In the hammer bank assembly, each hammer is situated between a pair of stationarily mounted flat permanent magnets. When a current flows through the coil, the resultant magnetic field interacts with the field of the permanent magnet, resulting in a force which propels the hammer towards the type font and the medium being printed. The basic configuration and operation of such a printing hammer is set forth in U.S. Pat. No. 3,279,362 to Helms, also assigned to Dataproducts Corporation. Other hammers are shown in U.S. Pat. No. 3,279,364, to Helms, U.S. Pat. No. 3,643,595 to Helms, et al and U.S. Pat. No. 3,983,806 to Ishi.
Print hammers and hammer bank assemblies of the type disclosed above have proven to be very effective in use, have exhibited high reliability and long lifetime as measured in the number of impact operations between replacement, and have gained widespread acceptance. However, new designs for hammer bank assemblies require hammers which have an even longer lifetime and which exhibit different operating characteristics than prior art hammers. Specifically, in the prior art, hammer bank assemblies were designed such that the crossed spring wires were flat and very rigid in the horizontal direction, thus preventing any side to side motion of the hammers. The body of each hammer was located between a pair of magnets, and the rigidity of the crossed spring wires served to keep the body in the correct position between two magnets. If, however, the body of the hammer were to come in contact with the side of a magnet, the friction between the body and the magnet would interfere with the performance of the hammer. Therefore, it was critical that the hammers be accurately mounted so as to not contact either of the magnets which surround them.
In contrast to the hammers used in prior art assemblies, it is an object of the present invention to achieve a hammer which is relatively flexible from side to side. This flexibility enables the hammer bank assembly to be designed so that the hammers are normally biased against the magnets. Because of the flexibility, the normal force and the friction between the magnets and hammers is relatively very low.
Further objectives of the present invention include the following:
(1) the further strengthening of the different components of the hammer;
(2) the elimination of some components of prior art hammers;
(3) the elimination of flat wire, formed springs;
(4) the elimination of close manufacturing tolerances of certain hammer components;
(5) the controlling of friction between the hammers and magnets.